This mod is, to put it lightly, AWESOME. What this does is fix a lot of things in minecraft’s code that notch hasn’t had time to fix yet or hasn’t found yet. It increases the FPS of the game on most computers, but more so on slower and less powerful computers. Gains of 20 FPS are normal.
If you find this helpful, you may want to try my other mod, McRegion, for reducing chunk load/save lag.
EDIT: McRegion is now built into Minecraft as of Beta 1.3
Credit goes to Scaevolus of the Minecraft Forums
FastRender: more efficient chunk queue processing.
UniText: a completely rewritten text renderer. It’s faster and supports Unicode, although the Unicode font files are not included with this release.
Fewer glClears: erasing the entire screen is expensive. This mod avoids it when possible.
Better chunk drawing code: Removing a few useless transforms from the chunk rendering code lets all visible chunks be drawn in a straightforward manner.
Better Tesselation: Modified for speed. TNT explosions no longer cause clients to have horrible lag, and everything in general should feel faster.
Error handling: Don’t go to a black screen when there’s an OpenGL error. Print a decent error message to the command line instead.
Optimine Minecraft Mod,
1) Locate your minecraft.jar file. On Windows, it’s in %APPDATA%/.minecraft/bin
2) Create a backup of minecraft.jar
3) Open minecraft.jar in an archive editor (WinRar/7-Zip/etc)
4) Delete the META-INF folder.
5) Copy the files from the downloaded zip file into the jar file, replacing previous files.
6) Run Minecraft and test!